Serious ankle problems can be caused by a number of conditions, such as arthritis (e.g., osteoarthritis, rheumatoid arthritis), diabetes, trauma, accidents, or severe deformation. One solution is to replace the ankle joint with an implant or ankle prosthesis. However, prostheses often fail due to subsidence, wear, and loosening within a few years following implantation. There are also anatomical considerations that make such implants non-feasible in some cases. Poor results with prostheses have led many surgeons to abandon implant arthroplasty in more serious cases and return to ankle arthrodesis—fusing the joint to ultimately result in bone fusion. Often, by the time fusion is selected as the best option, there is minimal motion at the joint prior to surgery.
Ankle fusion typically involves using screws and pins to hold the bone together. In a typical fusion surgery, the ankle joint is fused, allowing the tibia (shinbone) to grow together or fuse with the talus bone, the bone of the ankle that articulates with the tibia and fibula, and the calcaneus, the bone that forms the ankle joint. A long ankle arthrodesis “nail” may be inserted through the heel and fixed into place with screws or pins. Often, one or more screws or pins are inserted into the calcaneus, the bone at the lower back part of the foot forming the heel, which provides more stability.
Many of the currently available ankle fusion systems are less than optimal. One reason is because the screws or pins used to fuse the foot bones are secured only into the foot bones themselves; they are not secured to the ankle arthrodesis nail through which they are received. In some instances, an unsecured screw or pin can dislodge itself from the patient's bone and migrate out over years of use. Thus, there is a need in the art to provide a better solution to reduce the risk of migration.
Another reason that many of the currently available fusion systems are less than optimal is because they do not have angled fastener-receiving holes that allow for multi-planar fixation. Alternatively, if angled holes are present, they are not provided at optimal angle ranges for securing and immobilizing the ankle.
In some commercially available systems, the center of the fastener-receiving hole opening(s) in the ankle arthrodesis nail is perpendicular to the longitudinal axis of the nail, such that when the fastener is inserted, it is also perpendicular to the nail. This does not allow the surgeon to achieve purchase into preferred bones of the foot, but instead, limits the surgeon to securing the fastener into the calcaneus (the heel bone). Such systems also fail to provide the option of inserting fasteners in multiple axes to provide a more stable fixation system.
Moreover, fusion systems typically include one or more fasteners that engage only one foot bone in use. The fasteners do not cross articulating surfaces. It would be advantageous to provide a system that allows one or more fasteners to cross one or more articulating surfaces of the bones in the foot in order to provide more stability.
Another disadvantage of some fusion systems is that they do not provide nails with reinforced distal portions. If the nail is the same diameter throughout its length, but there are fastener holes in the distal portion, the implant may be weaker at that portion due to increased stresses from the patient's weight. Thus, there is a need for a fusion system that provides greater rigidity and stability in use.
Accordingly, it would be advantageous to provide a nail and fastener assembly that addresses many of the problems that have not been solved by currently-available systems.